As is known, to produce folders or covers, a flat blank is fed along a forming path through a number of forming stations, in each of which the blank is subjected to a specific operation, e.g. folding, gumming, pressing, etc.
As is known, to feed the blank along said path, conveyor belt assemblies are used, which, depending on the application, comprise a single conveyor belt looped about a powered roller and a return roller, or a number of separate powered conveyor belts smaller across than the single conveyor belt, arranged side by side, and an adjustable distance apart to adapt the supporting area to the size of the blanks.
The blanks are secured in position on the delivery branch/es of the conveyor belt/s using pressure devices, featuring rollers or single or side by side wheels, which are fitted to respective structures or frames separate from the conveyor, and are connectable directly by the machine operator to a fixed structure, depending on the article being produced. Again depending on the article being produced, the operator positions and locks helical or plate-type folding members on the conveyor belts.
Though widely used, known machines of the above type are unsatisfactory, mainly on account of the blanks nevertheless skidding laterally as they are conveyed. That is, in known machines, the travelling direction of the blanks does not always coincide with the theoretical direction, thus resulting in errors in both the shape and size of the finished articles. This is substantially due to assembly of the pressure devices on the belt conveyor/s, and particularly perfect perpendicularity between the travelling direction of the belt/s and the axes of rotation of the pressure rollers or wheels, substantially depending on the skill and experience of the machine operator. Moreover, the initial position of both the pressure devices and folding devices is not always maintained, on account of the construction characteristics of the device supporting structures and the connections inevitably working loose.
Moreover, in known machines, the position of the blanks along the feed path is determined by means of optical detectors. Using a single conveyor belt prevents the optical devices from being installed underneath the delivery branch of the conveyor, makes it difficult for the blank to be detected over the delivery branch, by preventing the use of through-beam optical detectors, and prevents the blank from being worked on from underneath the delivery branch of the belt.
Though enabling work on the blank from underneath the delivery branches, single conveyor belts pose other problems, due to each belt requiring its own supporting structure and drive assembly, and the various drive assemblies having to be perfectly synchronized to avoid lateral slippage and undesired stress on the blanks. Moreover, the distance between adjacent belts must be adjusted alongside changes in the size and/or shape of the blanks, and therefore at each production change, thus resulting in considerable cost in terms of machine stoppages.
Using conveyor belts in general also involves drawbacks when the machine comprises adhesive dispensers; in which case, any delay in cutting off supply results in adhesive being deposited directly on the belt, thus fouling the belt and invariably gumming together the incoming blanks.